In current practice dry-formed fibrous webs are prepared by dispensing a loose continuum of fibers onto a moving foraminous support surface to form a loose web. Because the loose web as intitally laid lacks integrity, a binding agent must be incorporated into the final web product. One method of incorporation admixes a particulate adhesive with the fibers prior to their deposition onto the forming surface, the adhesive subsequently being activated by application of moisture and/or heat. In another method adhesive is sprayed onto the fibers as they are airborne within the distributor, or as they are in transit from the distributor to the forming surface. Yet another technique is to dry-lay the fibers onto a moving foraminous wire, and subsequently to spray a binder solids bearing emulsion onto each side of the loose fibrous web, each application of the spray being followed by a drying step to at least partially dry and perhaps partly cure the binder. If necessary, the bonded web is finally heated to completely cure the fibrous web product. An improved embodiment of this latter technique is described in the commonly assigned pending patent application Ser. No. 108,022 filed Dec. 28, 1979 entitled "Methods of Applying Bonding Materials Onto Fibrous Webs."
The use of spray nozzles as described in U.S. Ser. No. 108,022, even with the utilization of vacuum to promote penetration, has several inherent disadvantages. Nozzles tend to plug with binder solids resulting in non-uniform coverage of the bonding material. While this problem is alleviated by larger sized nozzles, such nozzles cause greater usage of binder material. Further, the spray itself is not completely uniform in that is comprises discreet droplets of bonding agent, said droplets imparting to the web a mottled or dimpled appearance. At high nozzle discharge velocities, especially as such may develop with partially plugged orifices, the force of the droplets onto the web can compromise web integrity notwithstanding the presence of the bonding agent. To ensure a completely covered web, the spray area must extend beyond the outer edge of the web, including therefor portions of the carrier wire itself. This increases clean-up requirements and costs substantially, as well as the quantity of bonding agent used. Finally, the airborne or atomized spray cannot be confined, and eventually covers other parts of the apparatus thereby aggravating the clean-up problem.
In contradistinction to the spray nozzle means above described, the present invention utilizes extruder means to apply a continuous film of foamed binding agent onto the web. Unlike U.S. Pat. No. 4,159,355 granted to Kaufman, the applicator does not require an interior configuration of special design, but does have critical geometric relationships relating to its outlet dimensions.